A small program that plays when you're not using your computer screen, so that the screen is obscured from view. Traditionally used to save old-fashioned, obsolete monitors from damage caused by using too much light ('screen burn'), these are now used mostly for security and also for fun.

Things people who run websites do so that their sites are picked up by search engines and displayed near the top of search results. This can include making sure there are lots of keywords and links in every page.

An online service which will allow you to make long web addresses much shorter so that you can send them to people more easily. The website will create a new link on their own server which redirects to your link. The BBC uses a service called bit.ly to do this.

A small flat rectangular memory card which fits inside your mobile phone and which tells it basic information such as your phone number, and helps it connect to mobile phone networks. It can also include telephone numbers you have stored to your mobile phone's address book.

Code viewed in its most basic format (text) without being processed by your computer or browser. To view this web page's raw code in Internet Explorer or Firefox, click 'View' in the browser menu and select 'Page source' or 'Source'.